Splits a real number into a mantissa and exponent

#include <math.h>
double frexp ( double x , int *exp  );
float frexpf ( float x , int *exp  );         (C99)
long double frexpl ( long double x , int *exp  );         (C99)

The frexp( ) function expresses a floating-point number x as a normalized fraction f and an integer exponent e to base 2. In other words, if the fraction f is the return value of frexp(x, &e), then x = f x 2^e and 0.5 f < 1.

The normalized fraction is the return value of the frexp( ) function. The function places the other part of its "answer," the exponent, in the location addressed by the pointer argument. If the floating-point argument x is equal to 0, then the function stores the value 0 at the exponent location and returns 0.

Example

double fourthrt( double x )
{
  int exponent, exp_mod_4;
  double mantissa = frexp( x, &exponent );

  exp_mod_4 = exponent % 4;
  exponent -= ( exp_mod_4 ); // Get an exponent that's divisible by four ...
  for ( int i = abs( exp_mod_4 ); i > 0; i- )
  {
    if ( exp_mod_4 > 0 )     // ... and compensate in the mantissa.
      mantissa *= 2.0;
    else
      mantissa /= 2.0;
  }
  return ldexp( sqrt( sqrt( mantissa )), exponent / 4 );
}

See Also

The ldexp( ) function, which performs the reverse calculation.